JP6360446B2 - Rack shaft pressing mechanism - Google Patents

Description

  The present invention relates to a rack shaft pressing mechanism.

2. Description of the Related Art A vehicle steering apparatus includes a rack-and-pinion type that meshes a pinion gear and a rack gear and converts rotational movement of the pinion shaft accompanying steering operation into reciprocating movement of the rack shaft.
In such a rack and pinion type steering device, a rack shaft pressing mechanism (rack guide mechanism) for pressing the rack shaft against the pinion shaft is provided in order to reduce backlash between the pinion gear and the rack gear (Patent Documents below). 1 (see “Rack Shaft Support Device”).
The conventional rack shaft pressing mechanism includes a housing in which a housing chamber that opens toward the rack shaft is formed, a compression coil spring that is housed in the housing chamber, and a pinion that is biased by the compression coil spring to pin the rack shaft. A pressing member (rack guide) that presses against the shaft.

Further, in the conventional rack shaft pressing mechanism, the outer peripheral surface of the pressing member and the inner peripheral surface of the housing are prevented from coming into contact with each other to prevent contact noise from being generated. An annular elastic body is externally fitted.
Further, in order to set the frictional force between the elastic body and the inner peripheral surface of the housing to a predetermined value, the compression amount (tightening margin) of the elastic body compressed between the outer peripheral surface of the pressing member and the inner peripheral surface of the housing is set. It is adjusted.

JP 2005-132287 A

  By the way, since the rack shaft and the wheel are connected via the tie rod, the external force input to the wheel may be transmitted to the rack shaft, and the rack shaft may be separated from the pinion shaft. In such a case, the pressing member moves from the assembly position to the bottom surface side of the storage chamber, and then returns to the pinion side by the elastic force of the compression coil spring. When the pressing member returns to the pinion gear side, the rack gear pressed by the pressing member strongly collides with the pinion gear, and a relatively loud sound may be generated.

  On the other hand, although the compression amount (tightening allowance) of the elastic body can be increased to increase the frictional force, the speed at which the pressing member returns to the pinion side (hereinafter referred to as “return speed”) is increased. And the followability of the pressing member to the rack shaft is impaired. Therefore, it has been desired to develop a rack shaft pressing mechanism that gradually reduces the return speed of the pressing member when the pressing member returns to the assembly position from the bottom surface side of the storage chamber.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a rack shaft pressing mechanism in which the return speed of the pressing member is gradually reduced.

  In order to solve the above-described problems, a rack shaft pressing mechanism according to the present invention includes a housing in which a housing chamber that opens toward the rack shaft is formed, a compression coil spring that is housed in the housing chamber, and the housing chamber. A pressing member that is urged by the compression coil spring and presses the rack shaft against the pinion shaft, and an annular first elastic body and an annular second elastic body that are externally fitted to the pressing member. The second elastic body is positioned closer to the bottom surface side of the housing chamber than the first elastic body, and compresses the first elastic body with the outer peripheral surface of the pressing member on the inner peripheral surface of the housing. The second elastic body is compressed by the first inner peripheral surface formed to have the same diameter in the axial direction and the outer peripheral surface of the pressing member, and the diameter gradually increases toward the bottom surface side of the storage chamber. And a second inner peripheral surface.

  According to the invention, since the second inner peripheral surface is tapered, the compression amount (tightening allowance) of the second elastic body gradually increases from the bottom surface side of the storage chamber toward the assembly position. That is, when the pressing member returns to the assembly position, the elastic force of the second elastic body gradually increases, and the frictional force between the second elastic body and the second inner peripheral surface gradually increases. For this reason, the return speed of the pressing member is gradually reduced.

Furthermore, according to the invention, since the second inner peripheral surface is tapered, the direction of the drag (reaction force) of the second inner peripheral surface acting on the second elastic body is the second inner peripheral surface. Is inclined toward the bottom surface side of the storage chamber toward the central axis of the pressing member.
When this reaction force (reaction force) is disassembled into the radial direction and the axial direction of the pressing member, since the second elastic body has an annular shape, the radial component force is canceled out, and the axial direction (the bottom surface side of the storage chamber) Component force remains, and component force directed in the axial direction (bottom surface side of the storage chamber) acts on the pressing member.
And when a pressing member returns to an assembly position, since the drag (reaction force) of the 2nd inner peripheral surface which acts on the 2nd elastic body becomes large gradually, the axial direction (bottom side of a storage room) which acts on a pressing member The component power toward the will gradually increase. For this reason, the return speed of the pressing member is gradually reduced.
From the above, in addition to the frictional force, a component force directed in the axial direction (the bottom surface side of the storage chamber) also acts, so that the return speed of the pressing member is greatly reduced as it approaches the assembly position.

  In the invention, in the axial direction, the distance from the boundary between the first inner peripheral surface and the second inner peripheral surface to the first elastic body at the assembly position is determined by the pressing member at the assembly position. It is preferable that the distance is longer than the distance until it comes into contact with the bottom surface of the storage chamber.

  According to the said structure, even if a pressing member moves to the bottom face side of a storage chamber, the 1st elastic body is contact | abutting to the 1st internal peripheral surface. Therefore, when the pressing member returns to the assembly position, the pressing member moves smoothly without being rattled radially outward.

  In the invention, the diameter of the cross-sectional shape in the natural length of the second elastic body may be larger than the diameter of the cross-sectional shape in the natural length of the first elastic body.

  In the invention, a first recess in which the first elastic body is fitted and a second recess in which the second elastic body is fitted are formed on an outer peripheral surface of the pressing member, and the second recess is formed. The bottom surface of may be located radially outside the bottom surface of the first recess.

  Moreover, the said invention WHEREIN: The rectangular shape may be sufficient as the cross-sectional shape of a said 2nd elastic body.

  According to the present invention, it is possible to provide a rack shaft pressing mechanism in which the return speed of the pressing member is gradually reduced.

It is a schematic block diagram of an electric power steering device. It is sectional drawing which shows the structure of the rack guide mechanism which concerns on embodiment. It is sectional drawing which shows a state when a rack guide moves to the bottom face side of a storage chamber in a rack guide mechanism. It is the expanded sectional view which expanded the range enclosed with the broken line IV of FIG. It is sectional drawing which abstracted the range enclosed with the broken line V of FIG. It is sectional drawing which shows the structure of the rack guide mechanism which concerns on a 1st modification. It is sectional drawing which shows the structure of the rack guide mechanism which concerns on a 2nd modification.

  Embodiments of the present invention will be described with reference to the drawings. In the embodiment, an example in which the rack guide mechanism (rack shaft pressing mechanism) of the present invention is applied to an electric power steering apparatus will be described. However, the present invention is not limited to this, and the hydraulic type The present invention may be applied to a power steering device or a manual steering device.

  As shown in FIG. 1, the electric power steering apparatus 1 includes a steering mechanism 2 having a rack shaft 6 on which a first rack gear 5b on the steering wheel 4a side and a second rack gear 5c on the assist side are formed. It is a rack assist type device that includes an auxiliary torque mechanism 3 that applies a steering force.

The steering mechanism 2 includes a steering wheel 4a that is operated by the driver, a steering shaft 4b that is rotated by the operation of the steering wheel 4a, and a first pinion shaft 4c that is provided on the lower side of the steering shaft 4b via a torsion bar (not shown). The rack shaft 6 is connected to the left and right steering wheels 8 and 8 via tie rods 7 and 7 at both ends.
Further, the first pinion gear 5 a of the first pinion shaft 4 c meshes with the first rack gear 5 b of the rack shaft 6. When the driver rotates the steering wheel 4a, the rack shaft 6 moves to the left or right, and the steering wheels 8, 8 are steered.

The auxiliary torque mechanism 3 includes an assist motor 30, a worm gear mechanism 31, and a second pinion shaft 32 formed with a second pinion gear 32 a, and the second pinion gear 32 a of the second pinion shaft 32 is the rack shaft 6. It meshes with the second rack gear 5c.
The worm gear mechanism 31 includes a worm 33 that is pivotally attached to the assisting motor 30 and a worm wheel 34 that meshes with the worm 33. The worm wheel 34 is attached to the second pinion shaft 32. In the auxiliary torque mechanism 3, torque generated in the torsion bar is detected by a torque sensor (not shown), and the assist motor 30 is driven and controlled by a control device (not shown) in accordance with the detected torque. As a result, the torque generated by the assist motor 30 is transmitted to the rack shaft 6 as an auxiliary steering force via the worm gear mechanism 31 and the second pinion shaft 32.

As shown in FIGS. 2 and 3, the electric power steering apparatus 1 includes a rack guide mechanism 10 for reducing backlash between the first pinion gear 5 a and the first rack gear 5 b in the steering mechanism 2. .
In the present embodiment, an example in which the rack guide mechanism 10 is applied to the first pinion gear 5a and the first rack gear 5b in the steering mechanism 2 will be described. However, the present invention is not limited to this. The rack guide mechanism 10 according to the present invention may be applied to the second pinion gear 32a and the second rack gear 5c in the auxiliary torque mechanism 3, or the present invention is applied to both the steering mechanism 2 and the auxiliary torque mechanism 3. Such a rack guide mechanism 10 may be applied.

The rack guide mechanism 10 includes a housing 11 in which a storage chamber S opening toward the rack shaft 6 is formed, a compression coil spring 12 stored in the storage chamber S, and a storage coil S. A rack guide (pressing member) 13 that is biased to press the rack shaft 6 against the first pinion shaft 4c, a disc spring 14 that is housed in the housing chamber S, a first O-ring 16 that is externally fitted to the rack guide 13, and the first 2O ring 17.
Hereinafter, when the direction is described, the direction in which the storage chamber S extends is referred to as “axial direction”, the side on which the rack shaft 6 is disposed in the axial direction is referred to as “one end side”, and the opposite side is referred to as “the other end”. Referred to as “side”.

The housing 11 is for housing various components such as the first pinion shaft 4c and the rack shaft 6.
On the inner peripheral surface of the housing 11, a cylindrical first inner peripheral surface 11 a formed with the same diameter in the axial direction from one end side to the other end side, and a diameter increasing from one end side to the other end side. A tapered second inner peripheral surface 11b and a thread groove surface 11c are formed.

The first inner peripheral surface 11 a is a surface for compressing the first O-ring 16 in the radial direction in cooperation with the outer peripheral surface 13 e of the rack guide 13.
The second inner peripheral surface 11 b is a surface for compressing the second O-ring 17 in the radial direction in cooperation with the outer peripheral surface 13 e of the rack guide 13.
The thread groove surface 11c is a surface on which a thread groove is formed. And the screw 15 which comprises the bottom wall of the storage chamber S is screwing together in the screw groove of the screw groove surface 11c.

  Since the screw 15 is screwed into the screw groove of the screw groove surface 11c of the housing 11, when the screw 15 is rotated, the screw 15 is guided by the screw groove and moves to one end side or the other end side. In addition, the other end surface of the screw 15 is formed with an engagement hole 15a in which a jig (not shown) for rotating the screw 15 can be engaged.

  In assembling the screw 15, a distance (hereinafter referred to as "set length") L1 between one end surface of the screw 15 (hereinafter referred to as a bottom surface S1 of the storage chamber S) and a bottom surface 13c of a hole 13b described later of the rack guide 13 is described. Is adjusted to be shorter than the natural length of the compression coil spring 12.

  One end of the compression coil spring 12 contacts the bottom surface 13c of the rack guide 13, the other end contacts the bottom surface S1 of the storage chamber S, and the axial length of the compression coil spring 12 is compressed to the set length L1. . For this reason, the elastic force of the compression coil spring 12 always acts on the rack guide 13.

The rack guide 13 is a substantially cylindrical member, and is accommodated in the accommodation chamber S so that the central axis O extends in the axial direction.
One end surface 13 d of the rack guide 13 is in contact with the rack shaft 6. The one end surface 13d of the rack guide 13 is formed in a substantially semicircular arc shape corresponding to the outer peripheral surface of the rack shaft 6, and is restricted so that the rack shaft 6 does not move in the vertical direction.

The other end surface 13 a of the rack guide 13 is formed with a hole 13 b that opens toward the screw 15 and accommodates a part of the compression coil spring 12.
The compression coil spring 12 is in contact with the bottom surface 13c of the hole 13b of the rack guide 13, and the rack guide 13 is biased to one end side by the compression coil spring 12. For this reason, the rack guide 13 presses the rack shaft 6 against the first pinion shaft 4c, and the backlash between the first pinion gear 5a and the first rack gear 5b is reduced. Hereinafter, the position of the rack guide 13 in this state is referred to as an assembly position of the rack guide 13.

One end of the disc spring 14 is in contact with the other end surface 13 a of the rack guide 13, and the other end is in contact with the bottom surface S 1 of the storage chamber S. When the rack guide 13 is in the assembly position, the disc spring 14 is in a natural length state.
Therefore, as shown in FIG. 3, when the rack guide 13 is moved to the bottom surface S <b> 1 side of the storage chamber S, the disc spring 14 is compressed in the axial direction, and the rack guide 13 has other elastic force than the compression coil spring 12. Also, the elastic force of the disc spring 14 acts.
When the rack guide 13 is moved from the assembly position to one end side by L2 (see FIG. 2), the disc spring 14 is crushed and flattened. For this reason, the rack guide 13 hits the bottom surface S1 of the storage chamber S via the disc spring 14, and the movement of the rack guide 13 to the other end side is restricted.

The second O-ring 17 is located on the other end side (the bottom surface S1 side of the storage chamber S) than the first O-ring 16.
The first O-ring 16 and the second O-ring 17 are annular rubbers having a circular cross-sectional shape before assembly. Further, the first O-ring 16 and the second O-ring 17 are formed to have the same cross-sectional diameter before assembly.

  In order to prevent axial displacement between the first O-ring 16 and the second O-ring 17, the outer peripheral surface 13 e of the rack guide 13 has a first recess 18 into which the first O-ring 16 is recessed inward in the radial direction, A second recess 19 is formed on the inner side in the radial direction. The second recess 19 fits in the second O-ring 17.

The first recess 18 is formed at a position facing the first inner peripheral surface 11a when the rack guide 13 is in the assembly position.
As shown in FIG. 4, the distance L3 between the bottom surface 18a of the first recess 18 and the first inner peripheral surface 11a is smaller than the diameter of the cross-sectional shape of the first O ring 16 before assembly, and the first O ring 16 is compressed. ing.

Further, when the rack guide 13 is in the assembly position, the side surface 18b on the other end side of the first recess 18 is one end of the distance L4 from the boundary P between the first inner peripheral surface 11a and the second inner peripheral surface 11b. Away to the side.
Here, the distance L4 is larger than the distance L2 that the rack guide 13 in the assembly position can move toward the bottom surface S1 side of the storage chamber S (L4> L2). Therefore, even if the rack guide 13 moves to the bottom surface S1 side of the storage chamber S by the distance L2 (see the broken line in FIG. 4), the first O-ring 16 contacts the first inner peripheral surface 11a.

  As shown in FIG. 2, the second concave portion 19 is formed at a position facing the second inner peripheral surface 11 b when the rack guide 13 is in the assembly position. The bottom surface 19a of the second recess 19 is located radially outside the bottom surface 18a of the first recess 18 (see the auxiliary line H in FIG. 2).

As shown in FIG. 5, when the rack guide 13 is in the assembly position, the distance L5 between the bottom surface 19a of the second recess 19 and the second inner peripheral surface 11b is the diameter of the cross-sectional shape of the second O-ring 17 before assembly. And the second O-ring 17 is compressed.
Even if the rack guide 13 moves to the other end side by the distance L2 (see the broken line in FIG. 5), the distance L6 between the bottom surface 19a of the second recess 19 and the second inner peripheral surface 11b is the same as before assembly. The second O-ring 17 is compressed to be smaller than the diameter of the cross-sectional shape of the second O-ring 17.

  Next, the compression amount (tightening allowance) of the second O-ring 17 and the direction of the elastic force of the second O-ring 17 will be described with reference to FIG.

Since the 2nd inner peripheral surface 11b is formed in the taper shape, the distance (L5, L6) of the 2nd inner peripheral surface 11b and the bottom face 19a of the 2nd recessed part 19 is an assembly position from the bottom face S1 of the storage chamber S. The compression amount (tightening allowance) of the second O-ring 17 gradually increases.
For this reason, the elastic force (F11, F21) of the second O-ring 17 acting on the second inner peripheral surface 11b gradually increases, and the drag force (F12, F22) of the second inner peripheral surface 11b acting on the second O-ring 17 is also increased. It grows gradually.

Further, since the second inner peripheral surface 11b is tapered, the direction of the elastic force (F11, F21) of the second O-ring 17 is perpendicular to the second inner peripheral surface 11b, and the radial direction It is tilted toward one end toward the outside. For this reason, the direction of the drag (F12, F22) of the second inner peripheral surface 11b acting on the second O-ring 17 is inclined from the second inner peripheral surface 11b toward the central axis O of the rack guide 13 toward the other end side. ing.
Here, when the drag force (F12, F22) is decomposed into a first component force (F13, F23) directed radially inward and a second component force (F14, F24) directed axially, the first component force (F14, F24) is obtained. F13 and F23) cancel each other because the second O-ring 17 has an annular shape and acts on the entire circumference of the rack guide 13, and the second component force (F14 and F24) remains.
As a result, the second component force (F14, F24) acts on the rack guide 13.
The second component force (F24) when the rack guide 13 is in the assembly position is set to be smaller than the elastic force of the compression coil spring 12. Further, as a method of reducing the second component force (F24) acting on the rack guide 13, it is possible to use an O-ring having a small elastic force.

  Next, a case where an external force is input to the steering wheels 8 and 8 and the rack shaft 6 is separated from the first pinion shaft 4c will be described.

  When the rack shaft 6 is separated from the first pinion shaft 4c, the rack guide 13 is pressed by the rack shaft 6 and moves to the bottom surface S1 side of the storage chamber S. 3, the compression coil spring 12 and the disc spring 14 interposed between the rack guide 13 and the bottom surface S1 of the storage chamber S are compressed in the axial direction, and the elastic force of the compression coil spring 12 and the disc spring are compressed. The elastic force 14 acts on the rack guide 13.

  Here, as shown in FIG. 4, even if the rack guide 13 moves the distance L2 toward the bottom surface S1 of the storage chamber S, the first O-ring 16 is in contact with the first inner peripheral surface 11a. For this reason, when the rack guide 13 returns to the assembly position by the elastic force of the compression coil spring 12 or the like, the first O-ring 16 may slide on the first inner peripheral surface 11a, and the rack guide 13 may rattle radially outward. Absent.

As shown in FIG. 5, when the rack guide 13 returns to the assembly position by the elastic force of the compression coil spring 12 or the like, the second O-ring 17 slides on the second inner peripheral surface 11 b and the second O-ring 17 is compressed. The amount (tightening margin) increases gradually. For this reason, the drag (F12, F22) of the second inner peripheral surface 11b acting on the second O-ring 17 gradually increases.
Here, since the friction force (F15, F25) is proportional to the magnitude of the drag force (F12, F22) (F = μN: F is the friction force, μ is the friction coefficient, and N is the drag force), the second inner peripheral surface The frictional force between 11b and the second O-ring 17 also gradually increases (F25> F15). Therefore, the return speed of the rack guide 13 is gradually reduced.

  Further, when the rack guide 13 returns to the assembly position by the elastic force of the compression coil spring 12 or the like, the second inner peripheral surface 11b acting on the second O-ring 17 has a drag force (F12, F22) that gradually increases. The component forces (F14, F24) also gradually increase (F24> F14). Therefore, in addition to the frictional forces (F15, F25), the second component force (F14, F24) also acts, so that the return speed of the rack guide 13 is greatly reduced as the rack guide 13 approaches the assembly position.

As described above, according to the embodiment, when the rack guide 13 returns to the assembly position, in other words, the return speed of the rack guide 13 is greatly reduced as the rack shaft 6 approaches the first pinion shaft 4c. The magnitude of the hitting sound due to the contact between 6 and the first pinion shaft 4c is reduced.
Further, since the return speed of the rack guide 13 is gradually reduced, it is difficult to separate the rack guide 13 from the rack shaft 6 when the rack guide 13 returns to the assembly position. Therefore, the followability of the rack guide 13 with respect to the rack shaft 6 can be ensured.

Although the embodiment has been described above, the present invention is not limited to this.
For example, in the embodiment, rubber O-rings are used as the first elastic body and the second elastic body, but they may be made of resin.

  In the embodiment, the bottom surface 19a of the second recess 19 is formed so as to be positioned radially outward from the bottom surface 18a of the first recess 18. However, as shown in FIGS. The recesses (18A, 18B) and the second recesses (19A, 19B) are formed to the same depth, and the diameter of the cross-sectional shape of the second O-ring (17A, 17B) in the natural length is the cross-section in the natural length of the first O-ring 16 You may use a thing larger than the diameter of a shape. Further, as shown in FIG. 6, a second O-ring 17A having a rectangular cross-sectional shape may be used.

Further, in the embodiment, even when the rack guide 13 is moved to the bottom surface side of the storage chamber S, the second O-ring 17 is always in contact with the second inner peripheral surface 11b, but the present invention is limited to this. Not.
In the present invention, when the rack guide 13 returns to the assembly position, it is sufficient that the compression amount (tightening allowance) of the second O-ring 17 can be gradually increased, and the rack guide 13 contacts the second inner peripheral surface 11b in the middle of returning to the assembly position. You may do it.

  When the rack guide 13 is in the assembly position, the distance L5 between the bottom surface 19a of the second recess 19 and the second inner peripheral surface 11b is the distance between the bottom surface 18a of the first recess 18 and the first inner peripheral surface 11a. It may be smaller than L3. According to this, when the rack guide 13 is returned to the assembly position, the resistance force F11 and the second component force (F14, F24) are increased, and the hitting sound caused by the contact between the rack shaft 6 and the first pinion shaft 4c. Can be made smaller.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering mechanism 3 Auxiliary torque mechanism 4c 1st pinion shaft 5a 1st pinion gear 5b 1st rack gear 5c 2nd rack gear 6 Rack shaft 10 Rack guide mechanism (rack shaft pressing mechanism)
DESCRIPTION OF SYMBOLS 11 Housing 11a 1st internal peripheral surface 11b 2nd internal peripheral surface 11c Groove surface 12 Compression coil spring 13 Rack guide (pressing member)
15 Screw 16 First O-ring (first elastic body)
17, 17A, 17B Second O-ring (second elastic body)
18, 18A, 18B 1st recessed part 19, 19A, 19B 2nd recessed part 32 2nd pinion shaft 32a 2nd pinion gear

Claims (5)

A housing in which a storage chamber opening toward the rack shaft is formed;
A compression coil spring housed in the housing chamber;
A pressing member housed in the housing chamber and urged by the compression coil spring to press the rack shaft against the pinion shaft;
An annular first elastic body and an annular second elastic body that are externally fitted to the pressing member;
With
The second elastic body is located closer to the bottom surface side of the storage chamber than the first elastic body,
On the inner peripheral surface of the housing,
Compressing the first elastic body with the outer peripheral surface of the pressing member, and a first inner peripheral surface formed with the same diameter in the axial direction;
A tapered second inner peripheral surface that compresses the second elastic body with the outer peripheral surface of the pressing member and gradually expands in diameter toward the bottom surface side of the storage chamber;
A rack shaft pressing mechanism characterized in that is formed.   The distance from the boundary between the first inner peripheral surface and the second inner peripheral surface to the first elastic body at the assembly position in the axial direction is such that the pressing member at the assembly position is located on the bottom surface of the storage chamber. The rack shaft pressing mechanism according to claim 1, wherein the rack shaft pressing mechanism is longer than a distance to abut.   3. The rack shaft pressing according to claim 1, wherein a diameter of a cross-sectional shape in the natural length of the second elastic body is larger than a diameter of a cross-sectional shape in the natural length of the first elastic body. mechanism. On the outer peripheral surface of the pressing member, a first recess into which the first elastic body is fitted and a second recess into which the second elastic body is fitted are formed,
4. The rack shaft pressing mechanism according to claim 1, wherein a bottom surface of the second recess is positioned radially outward from a bottom surface of the first recess. 5.   The rack shaft pressing mechanism according to any one of claims 1 to 4, wherein a cross-sectional shape of the second elastic body is rectangular.

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